public Entry<K, V2> firstEntry() {
      return transformEntry(fromMap().firstEntry());
    }

    @Override
    @CheckForNull
    public Entry<K, V2> floorEntry(@ParametricNullness K key) {
      return transformEntry(fromMap().floorEntry(key));
    }

    @Override
    @CheckForNull
    public K floorKey(@ParametricNullness K key) {
      return fromMap().floorKey(key);
    }

    public Entry<K, V2> firstEntry() {
      return transformEntry(fromMap().firstEntry());
    }

    @Override
    @CheckForNull
    public Entry<K, V2> floorEntry(@ParametricNullness K key) {
      return transformEntry(fromMap().floorEntry(key));
    }

    @Override
    @CheckForNull
    public K floorKey(@ParametricNullness K key) {
      return fromMap().floorKey(key);
    }

    return keyOrNull(lowerEntry(key));
  }

  @Override
  @CheckForNull
  public Entry<K, V> floorEntry(K key) {
    return headMap(key, true).lastEntry();
  }

  @Override
  @CheckForNull
  public K floorKey(K key) {
    return keyOrNull(floorEntry(key));
  }

  @Override
  @CheckForNull
  public Entry<K, V> ceilingEntry(K key) {

        return nullableSynchronizedEntry(delegate().firstEntry(), mutex);
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> floorEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().floorEntry(key), mutex);
      }
    }

    @Override
    @CheckForNull
    public K floorKey(K key) {
      synchronized (mutex) {

        return nullableSynchronizedEntry(delegate().firstEntry(), mutex);
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> floorEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().floorEntry(key), mutex);
      }
    }

    @Override
    @CheckForNull
    public K floorKey(K key) {
      synchronized (mutex) {

    return keyOrNull(lowerEntry(key));
  }

  @Override
  @CheckForNull
  public Entry<K, V> floorEntry(K key) {
    return headMap(key, true).lastEntry();
  }

  @Override
  @CheckForNull
  public K floorKey(K key) {
    return keyOrNull(floorEntry(key));
  }

  @Override
  @CheckForNull
  public Entry<K, V> ceilingEntry(K key) {